Automotive disc brake

ABSTRACT

A disc brake for a hydraulic brake system of a motor vehicle is disclosed, which includes as customary a braking disc rotatable with a vehicle wheel, directly and indirectly actuated friction pad assemblies located adjacent to both sides of the braking disc and forced against the braking disc when fluid under pressure is supplied to the disc brake from a master cylinder and a yoke which is adapted to carry the pressure of the fluid to the indirectly actuated friction pad assembly, in which the improvement mainly comprises provision of means which takes a braking torque on the friction pad assemblies during operation whereby the yoke is freed of a duty of bearing the torque and permitted to serve only to carry the pressure of the working fluid to the indirectly actuated friction pad assembly, resulting in a simplified construction and a streamlined operation of the disc brake.

United States Patent 1 Toshida et al.

[ Nov. 20, 1973 AUTOMOTIVE DISC BRAKE [75] Inventors: Shunichi Toshida,Tokyo; Tadashi Kuroki, Yokohama; Nobutaka Someya, Tokyo; Tadashi Yano,Tokorozawa; Takashi Ozora, Tokyo, all of Japan [73 Assignee: NissanMotor Company,

X99949? 5 1 so "W.

221 Filed: May 10, 1971 21 Appl. No.: 141,487

FOREIGN PATENTS OR APPLICATIONS 968,898 9/1964 Great Britain 188/725Primary Examiner-George E. A. I-Ialvosa Attorney-McCarthy, Depaoli,OBrien & Price 57 ABSTRACT A disc brake for a hydraulic brake system ofa motor vehicle is disclosed, which includes as customary a braking discrotatable with a vehicle wheel, directly and indirectly actuatedfriction pad assemblies located adjacent to both sides of the brakingdisc and forced against the braking disc when fluid under pressure issupplied to the disc brake from a master cylinder and a yoke which isadapted to carry the pressure of the fluid to the indirectly actuatedfriction pad assembly, in which the improvement mainly comprisesprovision of means which takes a braking torque on the friction padassemblies during operation whereby the yoke is freed of a duty ofbearing the torque and permitted to serve only to carry the pressure ofthe working fluid to the indirectly actuated friction pad assembly,resulting in a simplified construction and a streamlined operation ofthe disc brake.

PAYENTEUNUYFO ms 3.773.149 SHEET 10F 3 MT, 0 784 Mm Pr ce ATTQRNEYSPAIENIEflnnvzo I975 3.773.149 SHEET 3 m 3 INVENTORS SAUDICJH 705L143)110 1421 SOTTICYE) '(wdash: Yano 7akvshl OzOra BY ATTORN EYS AUTOMOTIVEDISC BRAKE This invention is generally concerned with a hydraulic brakesystem of a motor vehicle and has a particular reference to a disc brakefor use in the brake system.

The disc brake in which the improvements according to this invention areto be incorporated is disclosed in the issued U. S. Pat. No. 3,245,500patented Apr. 12, I966.

The disc brake of the disclosed type uses a braking disc which isrotatable with a wheel of the motor vehicle and a stationary hydrauliccylinder which is open at both ends and which is secured to a stationarypart adjacent to one side of the braking disc. Two opposed pistons areaxially slidably fitted in the cylinder bore of the hydraulic cylinder,defining a fluid chamber therebetween. The fluid chamber communicateswith a brake pedal operated master cylinder or other source ofpressurized fluid and, when the brake pedal is depressed, the fluidunder pressure is supplied to the fluid chamber for urging the pistonsapart. A pair of friction pad assemblies are provided, one of which isinterposed between the hydraulic cylinder and the adjacent face of thebraking disc and the other is positioned adjacent the opposite face ofthe braking disc. The two pistons are respectively associated with thetwo friction pad assemblies in such a manner that one piston is inabutting engagement with one friction pad assembly to directly move theassembly toward the braking disc and the other piston is mechanicallyconnected to the other friction pad assembly so as to move this assemblythrough the mechanical connection toward the disc. Such mechanicalconnection is provided by a yoke which is connected to the indirectlyactuated friction pad assembly and on which the piston associated withthe indirectly actuated friction pad assembly bears when moved by thepressurized fluid supplied into the fluid chamber. The yoke is providedwith a central opening which is adapted to accommodate an adjacentarcuate portion of the braking disc and to form spaced side edges whichare parallel to the axis of the braking disc. Two opposed grooves areformed in the sides of an extension of the stationary hydraulic cylinderand receive the respective side edges of the opening in the yoke forslidably guiding the yoke in a direction parallel to the axis of thedisc.

The friction pad assemblies are forced against both faces of the brakingdisc when the pistons are moved apart by means of the pressurized fluidand, when this occurs, a braking torque is exerted on the friction padassemblies due to the traction applied thereto. In this instance, thebraking torque on the indirectly actuated friction pad assemblies istaken by the yoke which, in turn, transfers the torque to the stationaryhydraulic cylinder. The yoke is thus used not only to carry the movementof the piston to the indirectly actuated friction pad assembly but tobear the braking torque exerted on this pad assembly.

For simplicity of construction and to streamline the operation of thebrake, however, it is evidently desirable that the yoke be freed of aduty of bearing the braking torque and permitted to solely serve thepurpose of carrying the movement of the piston to the indirectlyactuated friction pad assembly.

Provision, moreover, of the side edges which are received in the opposedgrooves in the extension of the stationary hydraulic cylinder isreflected by a relatively large outside diameter of the hydrauliccylinder and by restrictions which are encountered in bending orpressmachining the yoke during production.

It is, therefore, a primary object of this invention to provide a discbrake in which the yoke is freed of the duty of receiving the brakingtorque on either of the friction pad assemblies and accordinglypermitted to solely serve the purpose of carrying the movement of one ofthe pistons to the indirectly actuated friction pad assembly. The discbrake according to this invention thus features a simplifiedconstruction and streamlined operation. As a means to achieve thisparticular object, the invention proposes to incorporate a stationarysupport structure which is connected to the hydraulic cylinder or to anystationary member of the motor vehicle. The support structure isprovided with an opening defining opposed internal side faces whichconfront side edges of the directly and indirectly actuated friction padassemblies which consequently bear at their side edges against theopposed side faces of the support structure when the friction padassemblies are forced against the faces of the braking disc. The brakingtorques on the friction pad assemblies are in this manner transferred tothe stationary support structure. The stationary support structure maybe secured to the hydraulic cylinder where the hydraulic cylinder isfast on a stationary member of the motor vehicle. Where the hydrauliccylinder having a bottom wall is movable, the support structure may besecured directly to the stationary member of the motor vehicle. In thisinstance, means may be provided which is adapted to support and guidethe hydraulic cylinder.

A secondary object of this invention is to provide a disc brake fromwhich the cooperating side edges and grooves provided for slidablyguiding the yoke can be removed where desired thereby to reduce theoutside diameter of the hydraulic cylinder and to facilitate bending orpress-machining of the yoke during production.

A further secondary object of this invention is to provide a disc brakein which arrangements are made so that an easy access to the frictionpad assemblies is provided to facilitate inspection and replacement ofthe friction pad assemblies. This will prove advantageous for timely andeasy maintenance and servicing of the disc brake.

Some practical forms of the disc brake in accordance with this inventionare illustrated by way of example in the accompanying drawings, inwhich:

FIG. 1 is a view illustrating in section in the left half and in plan inthe right half one form of the disc brake according to the invention;

FIG. 2 is a plan view, partly in section, of a portion of the disc brakeshown in FIG. 1',

FIG. 3 is a cross sectional view of the disc brake shown in FIG. 1;

FIG. 4 is similar to FIG. 1 but shows another form of the brakeaccording to the invention;

FIG. 5 is a side elevational view of the disc brake shown in FIG. 4; and

FIG. 6 is also similar to FIG. 1 but shows still another form of thedisc brake according to the invention.

Reference is now made to the drawings and particularly to FIGS. 1 to 3showing a first preferred embodiment of this invention in which theimprovements are made over the disc brake disclosed by the previouslynamed issued U. S. Pat. No. 3,245,500. Though not shown, the disc brakeis used in conjunction with a brake pedal operated master cylinder orother suitable source of fluid under pressure so as to apply brakes tothe wheels of a motor vehicle.

As illustrated, the disc brake includes a rotatable braking disc whichis mounted for rotation with the wheel through mechanical connectionsincluding, for instance, a member 11, bolts 12 and 13, a wheel disc 14and a rim 15 of the wheel. Adjacent an inner face of the braking disc 10is positioned a hydraulic cyliner 16 which, in this embodiment, is heldstationary through rigid connection with a stationary structural member11 through suitable fastening means such as a bolt 12'. This is bestseen in FIG. 3. As best seen in FIG. 1, the stationary hydrauliccylinder 16 is open at both ends and positioned to have its axissubstantially parallel to the axis of the braking disc 10. Inner andouter pistons 17 and 18, respectively, are axially slidably fitted inthe cylinder bore of the stationary hydrau lic cylinder 16. The pistonsI7 and 18 have opposed walls 17a and 180, respectively, so as to definea fluid chamber 19 therebetween. The fluid chamber 19 communicates withthe master cylinder (not shown) so that fluid under pressure is suppliedthereto when the brake pedal is depressed, whereby the pistons 17 and 18are urged apart from each other Directly and indirectly actuatedfriction pad assemblies are positioned adjacent the faces of the brakingdisc 10. The directly actuated friction pad assembly is interposedbetween the braking disc 10 and the stationary hydraulic cylinder 16 andcomprises a friction pad 20 and a backing plate 21 to which the frictionpad is bonded or otherwise secured. The inner piston 17 is thus inabutting engagement with the inner face of the backing plate 21. Theindirectly actuated friction pad assembly is positioned adjacent theopposite side of the braking disc 10 and comprises a friction pad 22 anda backing plate 23 secured thereto. The backing plates 21 and 23 maypreferably have larger areas than the respective friction pads 20 and22, as illustrated.

The stationary cylinder and the friction pad assemblies are housed in ayoke 24 which is generally a flat plate and which is partly raised as at24a (FIG. 3) to accommodate the adjacent arcuate portion of the brakingdisc 10. The yoke 24 has a suitably shaped opening 24b which forms agenerally rectangular tongue 244:. The tongue 24c is adapted to bereceived in the outer piston 18 so that the bottom wall 18a of thepiston bears against the forward end of the tongue 24c. An interlockingmember 25 is mounted on the yoke 24 and connected to the backing plate23 of the indirectly actuated friction pad assembly, which isconsequently interlocked with the yoke 24. Designated by referencenumerals 26 and 26 are sealing rings which are mounted between thehydraulic cylinder 16 and the two pistons 17 and I8.

When, now, the brake pedal is depressed and the fluid under pressure issupplied from the master cylinder into the fluid chamber 19 between theopposite walls 17a and 18a of the inner and outer pistons 17 and 18,respectively, then the pistons are moved apart from each other by meansof the fluid pressure. The inner piston 17 thus presses upon the backingplate 21 of the directly actuated friction pad assembly, forcing thefriction pad 20 against the braking disc 10. The outer piston 18, on theother hand, is moved away from the inner piston 17 and bears upon theforward end of the tongue 240 of the yoke 24. The yoke 24 is accordinglymoved in the direction of movement of the outer piston 18 with theresult that the indirectly actuated friction pad assembly is movedtoward the braking disc 10. The braking disc 10 is in this mannerpowerfully gripped by the two friction pads 20 and 22, to apply brake tothe wheel.

According to this invention, now, a support structure 27 is provided,which is securely mounted on the stationary hydraulic cylinder 16 bysuitable fastening means such as bolts 28 and 28'. The support structure27 has formed therein an opening 29 which is so configured as tosubstantially follow the outline of the friction pad assemblies toreceive therein the pad assemblies as clearly seen in FIG. 2. Theopening 29 may include two opposed guide grooves 29a and 29b receivingthe side edges of the backing plates 21 and 23 of the directly andindirectly actuated friction pad assemblies, respectively, so that thepad assemblies are guided when moved toward and away from the brakingdisc 10. The support structure 27 may also have formed therein a slot 30which is adapted to accommodate the adjacent arcuate portion of thebraking disc 10.

When the friction pad assemblies are forced against the faces of thebraking disc during braking action, the pad assemblies are subjected totraction due to the braking torque applied thereto from the braking discand, as a result, the backing plates 21 and 23 are forced against eitherof the side edges forming the opening 29. The braking torque is thustaken by the support structure 27 and is passed therethrough to thestationary hydraulic cylinder 16, while the yoke 24 isolated from thetorque at any instant. The yoke 24 is in this manner permitted to lenditself to solely carrying the movement of the outer piston 18 to theindirectly actuated friction pad assembly.

If desired, a slot 31 having a width in an axial direction related tothe combined axial thickness of the braking disc and the two frictionpad assemblies so as to provide a visual access to the pad assembliesmay be formed in the support structure 27 to facilitate inspection ofthe pads and backing plates. When the friction pads are found to haveworn out or to be destroyed, the friction pad assemblies can be replacedwith new ones simply by unscrewing the bolts 28 and 28 to remove thesupport structure 27 from the cylinder 16.

Another form of the disc brake according to this invention isillustrated in FIGS. 4 and 5. This modified disc brake functionsessentially similarly to the previously described form of the discbrake.

The disc brake of FIGS. 4 and 5 thus also includes directly andindirectly actuated friction pad assemblies surmounting both sides of arotatable braking disc 10. The directly actuated friction pad assemblycomprises a friction pad 20 and a backing plate 21, while the indirectlyactuated friction pad assembly comprises a friction pad 22 and a backingplate 23, similarly to the counterparts of the disc brake of FIGS. 1 to3. A guide pin 32 is passed through apertures formed in the backingplates 21 and 23, guiding the friction pad assemblies when the padassemblies are moved toward and away from the braking disc.

In this modified form of the disc brake, a hydraulic cylinder which isnow represented by numeral 33 is positioned adjacent to the inner faceof the backing plate 21 of the directly actuated friction pad assembly.Working in the cylinder 33 is the piston, which is sealed by a sealingring 37 housed in an annular groove in the cylinder bore and which is inabutting engagement with the backing plate 21. Between the bottom wall34 of the cylinder 33 and an outer face of the piston 35 is defined afluid chamber 36 which communicates with the master cylinder to receivetherefrom fluid under pressure when the brake pedal is depressed. Thepressurized fluid supplied into the fluid chamber 36 acts upon thecylinder 33 and the piston 35 which are consequently moved apart fromeach other. Designated by reference numeral 38 is dust-proofing sealmeans which may be provided at the innermost ends of the cylinder 33 andthe piston 35 so as to preclude entrance of dust into the cylinder.

The cylinder and the friction pad assemblies are encased in a yoke 39.The yoke 39 is substantially centrally opened to form lengthwise edges39a and 39b facing the outer face of the bottom wall 3 3 of the cylinder33 and the outer face of the back plate 23 of the indirectly actuatedfriction pad assembly. With this arrangement, when the cylinder 33 ismoved away from the piston 35 by the fluid pressure drawn into the fluidchamber 36 it bears at its outer face upon the lengthwise edge 39a ofthe yoke 39 so as to move the yoke in the same direction. The yoke 39,in turn, presses at its lengthwise edge 39b upon the backing plate 23 ofthe indirectly actuated friction pad assembly. The indirectly actuatedfriction pad assembly is consequently forced against the outer face ofthe braking disc 10. The directly actuated friction pad assembly, on theother hand, is moved to the braking disc by the pressure exerted theretoby the piston 35 which is forced toward the braking disc by the fluidpressure in the fluid chamber 36.

The disc brake of FIGS. 4 and 5 now further includes a support structureby which the cylinder 33 is supported and guided when moved.

The support structure comprises a stationary support member 40 havingformed therein recesses 41 and 41. The recess 41 not only accommodatesthe arcuate portion of the braking disc 110 but receives therein thefriction pad assemblies in a manner to permit the pad assemblies to movein a direction parallel to the axis of the braking disc 10. The recess411 on the other hand, accommodates therein the cylinder 33. Morespecifically, the recess 41 defines a pair of opposite side edges 41aand 41b for abutting engagement with the sides of the directly actuatedfriction pad assembly and a pair of opposite side edges 41c and did forengagement with the sides of the indirectly actuated friction padassembly, as shown. Arms 42 are is secured to the support member 40 andextends toward the hydraulci cylinder 33. Each arm 42 has formed in itsfree end portion an aperture (not numbered) into which a guide pin 43 isslidably inserted through a bushing 44 which may be made of elasticmaterial such as rubber. The guide pin 43 is directed in parallel to thedirection of movement of the cylinder 33 and rigidly connected thereto.The pin 43 is herein illustrated as secured to the cylinder 33 throughlimbs 45 and 45 extending from the cylinder. The support number 40 isrigidly secured to a suitable stationary member 46 of the motor vehiclethrough suitable fastening means such as for instance a bolt 47 as seenin FIG. 5.

With the support structure arranged in this manner, when the frictionpad assemblies are forced against the braking disc 10 to apply brakes,the pad assemblies are caused to bear against either the side edges 41aand 41c or 41b and 41d of the support member 40 depending on thedirection of rotation of the braking disc. The braking torque impartedto the friction pad assemblies due to traction by the braking disc 10 istaken by support member 40 which, in turn, transfers the torque to thestationary member 46 of the motor vehicle. The yoke 33 is thereforeliberated from a duty of taking such braking torque during the brakingoperation and is permitted to solely contribute to carrying the movementof the cylinder 33 to the indirectly actuated friction pad assembly.

The use of the rubber bushing 44 to retain the guide pin 43 will provebeneficial for efficient movement of the cylinder 33 because of itselasticity that urges the guide pin 43 to return in a direction oppositeto the direction in which the guide pin has been moved with the cylinderby the fluid pressure.

The space over the friction pad assemblies is open in the disc brakeshown in FIGS. 4 and 5 to provide an easy access to the pad assemblies,facilitating inspection and replacement of the pad assemblies. The padassemblies can be removed and replaced with new ones simply by removingthe guide pin 32 from the assemblies. Provisions of such open space overthe pad assemblies will also prove advantageous for the purpose ofdissipating the heat evolved in the friction pads and the braking discdue to friction therebetween.

It will now be appreciated from the foregoing de scription that thefirst and second forms of the disc brake according to this invention areuseful] especially where a simplified construction and a streamlinedsmooth operation of the disc brake is a matter of concern. With thearrangements of the disc brake hereinbefore described, it is no longernecessary that the cylinder 16 or 33 be provided with a guide groove toengage the longitudinal side edge of the central opening which is formedin the yoke. This is advantageous not only for reducing the outsidediameter of the hydraulic cylinder but for simplifying the internal andexternal outlines of the yoke. The yoke thus features a compactconstruction and is adapted for being bent or pressmachined duringproduction.

A primary feature of the disc brake according to this invention is, aspreviously discussed, that the yoke is not required to take the brakingtorque on the friction pad assemblies. This feature can be maintainedeven in a disc brake using a yoke which slides on a stationary memberbecause no torque is transferred to the yoke through the slidingengagement between the yoke and the stationary member. An example of adisc brake of this character is illustrated in FIG. 6.

The disc brake shown in FIG. 6 is shown, by way of example, as amodification of the disc brake of FIGS. 1 to 3 and, as such, likereference numerals are assigned to corresponding members.

in the disc brake herein shown, the outer piston 18 is shown to beinverted to define the fluid chamber 19 between its cavity and theopposite wall of the inner piston 117 and a bear against the internallengthwise edge of the yoke 24 at its outermost wall 18a.

The support structure 27 is now provided with a guide groove 49 whichextends in a direction substantially parallel to the axis of the brakingdisc 110. Likewise, the yoke 24 has formed on its external side edge astraight sliding surface 50 which is received in the guide groove 49.The yoke 24 is thus guided by the groove 49 when moved in a directionparallel to the axis of the braking disc 10. In this instance, thebraking torque on the friction pad assemblies is transferred to thestationary hydraulic cylinder 16 through the support structure 27 and,as a consequence, the yoke 24 is completely isolated from such torque.

We claim:

1. A disc brake for motor vehicle hydraulic brake system, comprising:

1. a braking disc rotating with a wheel of the motor vehicle;

2. a hydraulic cylinder having a bottom wall;

3. a piston slidable in opposite directions which are substantiallyparallel to an axis of said braking disc, said piston and said cylinderdefining a fluid chamber into which pressurized fluid is supplied when abraking action is to be initiated;

4. directly and indirectly actuated friction pad assemblies surmountingboth sides of said braking disc, said directly actuated friction padassembly being in abutting engagement with said piston and therebyforced against said braking disc when said piston is moved by saidpressurized fluid;

5. a yoke movable in a direction parallel to said axis of said brakingdisc and carrying the movement of said cylinder to said indirectlyactuated friction pad assembly for forcing said indirectly actuatedfriction pad assembly against said braking disc when said cylinder ismoved by said pressurized fluid, said yoke having a lengthwise edgewhich bears against said bottom wall of said cylinder;

6. a guide pin being passed through apertures formed in backing platesof said friction pad assemblies for guiding said friction pad assemblieswhen said friction pad assemblies are moved toward and away from saidbraking disc; and

7. a stationary support structure for supporting and guiding saidhydraulic cylinder, said support structure comprising a stationarysupport member having formed therein recesses and secured to astationary member of the motor vehicle, one of said recessesaccommodating an arcuated portion of said braking disc and receivingtherein said friction pad assemblies, while the other accommodatingtherein said cylinder, arms secured to said support member and having anaperture formed at its free end portion, and guide pins secured to saidcylinder and extending in a direction parallel to the direction ofmovement of said cylinder, each guide pin being slidably passed throughsaid aperture in said arm for supporting, and guiding said cylinder whensaid cylinder is moved.

2. A disc brake according to claim 1, wherein said support structurefurther comprises rubber bushings, each of which is secured in saidaperture in said arm.

3. A disc brake according to claim 1, wherein said yoke is open oversaid friction pad assemblies.

4. A disc brake according to claim 1, wherein dustproofing seal means isprovided at the innermost ends of said cylinder and said piston so as topreclude entrance of dust into said cylinder.

1. A disc brake for motor vehicle hydraulic brake system, comprising: 1.a braking disc rotating with a wheel of the motor vehicle;
 2. ahydraulic cylinder having a bottom wall;
 3. a piston slidable inopposite directions which are substantially parallel to an axis of saidbraking disc, said piston and said cylinder defining a fluid chamberinto which pressurized fluid is supplied when a braking action is to beinitiated;
 4. directly and indirectly actuated friction pad assembliessurmounting both sides of said braking disc, said directly actuatedfriction pad assembly being in abutting engagement with said piston andthereby forced against said braking disc when said piston is moved bysaid pressurized fluid;
 5. a yoke movable in a direction parallel tosaid axis of said braking disc and carrying the movement of saidcylinder to said indirectly actuated friction pad assembly for forcingsaid indirectly actuated friction pad assembly against said braking discwhen said cylinder is moved by said pressurized fluid, said yoke havinga lengthwise edge which bears against said bottom wall of said cylinder;6. a guide pin being passed through apertures formed in backing platesof said friction pad assemblies for guiding said friction pad assemblieswhen said friction pad assemblies are moved toward and away from saidbraking disc; and
 7. a stationary support structure for supporting andguiding said hydraulic cylinder, said support structure comprising astationary support member having formed therein recesses and secured toa stationary member of the motor vehicle, one of said recessesaccommodating an arcuated portion of said braking disc and receivingtherein said friction pad assemblies, while the other accommodatingtherein said cylinder, arms secured to said support member and having anaperture formed at its free end portion, and guide pins secured to saidcylinder and extending in a direction parallel to the direction ofmovement of said cylinder, each guide pin being slidably passed throughsaid aperture in said arm for supporting, and guiding said cylinder whensaid cylinder is moved.
 2. a hydraulic cylinder having a bottom wall; 2.A disc brake according to claim 1, wherein said support structurefurther comprises rubber bushings, each of which is secured in saidaperture in said arm.
 3. A disc brake according to claim 1, wherein saidyoke is open over said friction pad assemblies.
 3. a piston slidable inopposite directions which are substantially parallel to an axis of saidbraking disc, said piston and said cylinder defining a fluid chamberinto which pressurized fluid is supplied when a braking action is to beinitiated;
 4. directly and indirectly actuated friction pad assembliessurmounting both sides of said braking disc, said directly actuatedfriction pad assembly being in abutting engagement with said piston andthereby forced against said braking disc when said piston is moved bysaid pressurized fluid;
 4. A disc brake according to claim 1, whereindust-proofing seal means is provided at the innermost ends of saidcylinder and said piston so as to preclude entrance of dust into saidcylinder.
 5. a yoke movable in a direction parallel to said axis of saidbraking disc and carrying the movement of said cylinder to saidindirectly actuated friction pad assembly for forcing said indirectlyactuated friction pad assembly against said braking disc when saidcylinder is moved by said pressurized fluid, said yoke having alengthwise edge which bears against said bottom wall of said cylinder;6. a guide pin being passed through apertures formed in backing platesof said friction pad assemblies for guiding said friction pad assemblieswhen said friction pad assemblies are moved toward and away from saidbraking disc; and
 7. a stationary support structure for supporting andguiding said hydraulic cylinder, said support structure comprising astationary support member having formed therein recesses and secured toa stationary member of the motor vehicle, one of said recessesaccommodating an arcuated portion of said braking disc and receivingtherein said friction pad assemblies, while the other accommodatingtherein said cylinder, arms secured to said support member and having anaperture formed at its free end portion, and guide pins secured to saidcylinder and extending in a direction parallel to the direction ofmovement of said cylinder, each guide pin being slidably passed throughsaid aperture in said arm for supporting, and guiding said cylinder whensaid cylinder is moved.